1. Field of the Invention
This invention relates generally to improvements in continuously variable transmissions (CVTs) employed in vehicular applications. More particularly, the invention relates to an improved CVT that offers considerably reduced structural complexity compared to typical toroidal types of CVTs.
2. Description of the Prior Art
Automatically actuated electromechanical transmissions include actuation software modules of the embedded type, generally including connection links to engine control modules through standardized protocols. To the extent that the most new on-highway truck transmissions are actuated and controlled by software, they lend themselves to fully automated controls. As such, there has been considerable interest in providing CVT-like operating systems in trucks, motivated substantially by desire for improved economy of operation.
U.S. Pat. No. 6,085,606 issued Jul. 11, 2000 to Stine et al. provides an example of one such CVT-like transmission. That patent describes a 12-speed transmission which, although including gears, provides relatively small steps between the ratios of its highest ratio gears, gears 7–12, compared to the ratio steps between its lowest gears, 1–6. Thus, in its highest gear ratios, the behavior of the transmission approximates an actual CVT. Indeed, to the extent that on-highway trucks spend approximately 85–90 percent of their operating lives in their highest gear ratios, such accommodation involving only the highest gears has been deemed to be a suitable relatively inexpensive approach, though of course more limited than an actual CVT.
Thus, use of a CVT-like or “mock CVT” approach has been acceptable in that it generates significant benefits in fuel economy, while traditionally considerably cheaper to manufacture than significantly more expensive full CVT transmissions. Indeed, the presently emerging belt-type and toroidal CVT transmissions, even at today's levels of technology and development, are believed to be insufficient to accommodate and/or transmit the relatively high torques associated with on-highway trucks. Thus, a full, actual CVT transmission for trucks that could be manufactured relatively inexpensively, and that could operationally meet required torque demands, would be well received, particularly among truck fleet owners.